Conventionally, stuttering has been treated by several different types of treatment, including psychiatric therapy, drug therapy, and the use of altered auditory feedback, generated by electrical signal processing devices, relayed to the person who stutters. These techniques can be generally characterized as either endogenous alterations of the speech signal output or “motoric strategies”, such as prolonged or slowed speech, rhythmic speech, singing, and lipped speech, or exogenous dynamic alterations of the speech signal itself (“altered auditory feedback strategies”), both of which can successfully induce relatively fluent speech in people who stutter. See, e.g., O. Bloodstein, A Handbook on Stuttering (5th ed. Singular, San Diego, Calif., 1995). Unfortunately, the ameliorative effects of these phenomena are generally temporary and are thought to need to be engaged in relatively constantly to reduce stuttering frequency. See Kalinowski et al., Inducement of fluent speech in persons who stutter via visual choral speech, 280 Neuroscience Letters, pp. 1–3(Elsevier Science Ireland Ltd, 2000).
Two types of altered auditory feedback which have been used to treat stuttering include delayed auditory feedback (“DAF”) and the introduction of a masking noise or masked auditory feedback (“MAF”). Generally described, DAF imposes a delay on the delivery of a feedback speech signal to a speaker/stutterer, while MAF serves to compete with a speaker's auditory feedback.
For example, M. E. Wingate, in Stuttering: theory and treatment, p. 237 (Irvington, 1976), describes a type of altered auditory feedback which can include DAF to provide emphasis on phonation, i.e., slowing speech down to extend syllable duration. However, this type of auditory feedback or fluency enhancement is conventionally thought to be achievable with or without the use of DAF as long as syllable prolongation was employed. See, e.g., W. H. Perkins, From Psychoanalysis to Discoordination, in H. H. Gregory (Ed.) Controversies about stuttering therapy, pp. 97–127 (University Press, 1979). See also Andrew Stuart et al., Fluent Speech, Fast Articulatory Rate, and Delayed Auditory Feedback: Creating a Crisis for A Scientific Revolution?, 82 Perceptual and Motor Skills, pp. 211–218 (1996).
Generally stated, the reduction in stuttering frequency under speech signal alterations has been attributed to entrained rhythm, distraction, modified vocalization, and rate reduction. Indeed, in the past, slowed speech rates were found to be an important factor in the reduction of stuttering. For example, in W. H. Perkins et al., Phone rate and the effective planning time hypothesis of stuttering, 29 Jnl. of Speech and Hearing Research, 747–755 (1979), the authors reported that stuttering was virtually eliminated when speakers reduced speech rate by approximately 75%. However, other reports have found that rate reduction is neither necessary, nor sufficient, for fluency enhancement. See Kalinowski, et al., Stuttering amelioration at various auditory feedback delays and speech rates, European Journal of Disorders of Communication, 31, 259–269 (1996); Stuart et al., Fluent speech, fast articulatory rate, and delayed auditory feedback: Creating a crisis for a scientific revolution?, Perceptual and Motor Skills, 82, 211–218 (1996); MacLeod, et al., Effect of single and combined altered auditory feedback on stuttering frequency at two speech rates, Journal of Communication Disorders, 28, 217–228 (1995); Kalinowski et al., Effect of normal and fast articulatory rates on stuttering frequency, Journal of Fluency Disorders, 20, 293–302 (1995); Hargrave et al, Effect of frequency-altered feedback on stuttering frequency at normal and fast speech rates. Journal of Speech and Hearing Research, 37, 1313–1319 (1994); and Kalinowski et al., Effects of alterations in auditory feedback and auditory feedback and speech rate on stuttering frequency. Language and Speech, 36, 1–16 (1993).
Recently, a portable therapeutic device and related stuttering enhancement treatment methods were described in U.S. Pat. No. 5,961,443 to Rastatter et al., the contents of which are hereby incorporated by reference as if recited in full herein. These devices and methods employ altered auditory feedback (auditory delay and/or frequency shift signals) to be delivered to a stutterer via a portably configured device.